Looks like a recent downtime wrecked some games.
I had a Backgammon game with literally no dice (https://brainking.com/en/ShowGame?g=9526127&i=23), so I could only chose 'pass' (but that seemed to work), and now I have a Clone Backgammon game with no moves allowed because the bar point is missing or overfilled (https://brainking.com/en/ShowGame?g=9517616&i=226), there are 16 checkers there, which could also be a long-time bug? I tried to create the correct move url myself, but it doesn't work either - I need to bring in the hit checker from the bar, but I cannot. So it's resign, draw, or timeout....

update: I managed to make a move, by appending "ShowMove?g=9536172&m=26" to the url. The bar is '26', not '25', as I thought before. Turns out this is an old bug; whenever you have more than 15 checkers on the bar, it is not clickable anymore; there is no image for that count which makes the link generation fail. I had that same issue for several moves afterwards, until I was able to bring enough checkers in to get to 15 or less on the bar.
If that ever happens to you, add the above to your url (with *your* game's id of course).